--- On Tue, 6/9/09, Matthieu Brucher <matthieu.bruc...@gmail.com> wrote:
> Hi, > > Is it really ? > You only show the imaginary part of the FFT, so you can't > be sure of > what you are saying. Indeed, is there not a "label" for a function f which satisfies Im(iFFT(f)) = Im(FFT^2(f)), Re(iFFT(f)) != Re(FFT^2(f))? (And similarly if Im and Re roles are reversed.) Seems like the class of such functions (if any exist) might have some interesting properties... DG > Don't forget that the only difference between FFT and iFFT > is (besides > of teh scaling factor) a minus sign in the exponent. > > Matthieu > > 2009/6/9 bela <bela.miha...@gmail.com>: > > > > I tried to calculate the second fourier transformation > of an image with the > > following code below: > > > > > --------------------------------------------------------------- > > import pylab > > import numpy > > > > ### Create a simple image > > > > fx = numpy.zeros( 128**2 ).reshape(128,128).astype( > numpy.float ) > > > > for i in xrange(8): > > for j in xrange(8): > > fx[i*8+16][j*8+16] = 1.0 > > > > ### Fourier Transformations > > > > Ffx = numpy.copy( numpy.fft.fft2( fx ).real ) # 1st > fourier > > FFfx = numpy.copy( numpy.fft.fft2( Ffx ).real ) # > 2nd fourier > > IFfx = numpy.copy( numpy.fft.ifft2( Ffx ).real ) # > inverse fourier > > > > ### Display result > > > > pylab.figure( 1, figsize=(8,8), dpi=125 ) > > > > pylab.subplot(221) > > pylab.imshow( fx, cmap=pylab.cm.gray ) > > pylab.colorbar() > > pylab.title( "fx" ) > > > > pylab.subplot(222) > > pylab.imshow( Ffx, cmap=pylab.cm.gray ) > > pylab.colorbar() > > pylab.title( "Ffx" ) > > > > pylab.subplot(223) > > pylab.imshow( FFfx, cmap=pylab.cm.gray ) > > pylab.colorbar() > > pylab.title( "FFfx" ) > > > > pylab.subplot(224) > > pylab.imshow( IFfx, cmap=pylab.cm.gray ) > > pylab.colorbar() > > pylab.title( "IFfx" ) > > > > pylab.show() > > > --------------------------------------------------------------- > > > > On my computer FFfx is the same as IFfx..... but why? > > > > I uploaded a screenshot about my result here: > > http://server6.theimagehosting.com/image.php?img=second_fourier.png > > > > Bela > > > > > > -- > > View this message in context: > > http://www.nabble.com/second-2d-fft-gives-the-same-result-as-fft%2Bifft-tp23945026p23945026.html > > Sent from the Numpy-discussion mailing list archive at > Nabble.com. > > > > _______________________________________________ > > Numpy-discussion mailing list > > Numpy-discussion@scipy.org > > http://mail.scipy.org/mailman/listinfo/numpy-discussion > > > > > > -- > Information System Engineer, Ph.D. > Website: http://matthieu-brucher.developpez.com/ > Blogs: http://matt.eifelle.com and http://blog.developpez.com/?blog=92 > LinkedIn: http://www.linkedin.com/in/matthieubrucher > _______________________________________________ > Numpy-discussion mailing list > Numpy-discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion > _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion